A power tool, such as a drill/driver, generally has a transmission to transmit power from a motor to an output shaft of the tool. Such a transmission often functions to reduce the speed and increase the torque from the motor. This type of transmission generally operates at a constant speed ratio, meaning that the ratio between the speed of the output shaft and the motor remains generally constant. For example, the transmission may rotate the output shaft at 0.25 times the output speed of the motor. Examples of such a transmission include a parallel axis transmission with spur gears, and a planetary transmission with planetary gears.
Certain other power tools, such as impact drivers or impact wrenches, may additionally include a hammering mechanism known as a Pott mechanism disposed between the transmission or motor and the output shaft. Versions of a Pott mechanism are described, for example, in U.S. Pat. Nos. 2,012,916 and 2,160,150, each of which is incorporated by reference. Generally, a Pott mechanism is coupled to the output of a planetary gear transmission and includes a spring biased hammer that rides along V-shaped grooves in an anvil. The hammer applies a rotational hammering force to the output shaft when a certain threshold of torque is encountered by the output shaft. Thus, when hammering, the Pott mechanism applies rotational blows to the rotating output shaft to assist in driving fasteners through hard joints and inhibiting screwdriving bits from slipping out of the heads of screws (known as “cam-out”). However, the Pott hammering mechanism tends to be very noisy and causes a great deal of vibration.